This invention relates to an improved multifocal contact lens. More specifically this invention relates to a bifocal contact lens with enhanced near and distance vision characteristics.
Single vision contact lenses have been widely prescribed and successfully worn by the general population for years as an effective alternative to spectacle vision correction. As the population of contact lens wearers approaches the age of forty five or so, however, the physiology of the eye matures, becomes less elastic and loses its ability to focus at near or normal reading distance. This condition is known as presbyopia. The presbyopic population that had previously enjoyed the advantages of single vision contact lens have been highly motivated to continue and consequently have turned to the industry for bifocal contacts.
Unfortunately bifocal contact lenses appearing in the past have encountered certain difficulties, compromises and wearer limitations that has chilled presbyopic patient enthusiasm.
Presently there are three principal types of bifocal contact lenses: (1) simultaneous vision or concentric lenses (2) alternating vision lenses and (3) diffraction or halographic lenses.
Simultaneous vision lenses are physically symmetric in design and are manufactured with a central zone having a prescriptive power suitable for a patient's distant or far vision and a peripheral rim of a different prescriptive value for the patient's near vision. With this type lens a patient simultaneously views objects through both near and far corrective powers. While some presbyopes have been able to adapt well to this lens design, by the brain interpreting the correct image, it will be recognized that a tendency exists for blurring to occur.
In this connection many patients may experience a delay in focusing while others notice a flare around lights or ghost images; one image in-focus and one out-of-focus. This phenomena is exacerbated in instances of low or dim illumination because a wearer's pupil will dilate into the near vision peripheral zone of the lens. Still further, since the pupillary zone is only about three millimeters in diameter, simultaneous vision lenses must center perfectly for a patient to see through the proper area.
An improved simultaneous vision contact lens has now been developed which is often referred to as a holographic or diffraction bifocal lens. This lens comprises a plurality of closely spaced concentric prescriptive values from central distant vision to near vision at an outer periphery. The rings are contoured onto the back or concave surface of the lens. In this lens wavelets come to two focal points: near and distance. Potential limitations of this lens include visual acuity in dim illumination and some degree of continual haziness or blur due to the fact that out-of-focus light is continuously superimposed upon an image that is in focus.
Alternatively presbyopes have been fitted with alternating vision contact lenses which optically resemble bifocal spectacles with a superior segment being formed with a distant vision prescription and an inferior segment fashioned for near vision. In order to maintain the proper orientation of this lens it is necessary to utilize one of a variety of techniques such as prism ballasting, truncation, a combination of truncation and ballasting, and the like.
Although conventional alternate vision lenses can be effectively worn by patient's able to adjust to lens orientation techniques, there are at least some vision problems occasioned with straight ahead or elevated near vision. Specifically, straight forward or elevated near vision, such as might be frequently required by a plumber, painter, etc., dictates tilting one's head backward when wearing a typical alternating vision contact in order to focus through the inferior near vision portion of the lens.
While previously known multifocal contact lenses, such as described above, have achieved a degree of acceptance in the past, room for significant improvement remains. In this regard, it would be highly desirable to provide an enhanced bifocal contact lens which would enable a wearer to view near objects in a straight ahead posture. In a similar vein, it would be advantageous to enable a bifocal contact lens wearer to view objects in a vertically elevated near position without encountering the limitations previously discussed in connection with simultaneous vision lenses. Still further, it would be desirable to provide bifocal contact lens which would provide enhanced dim illumination without flare, ghosting or headlight halo. Yet further, it would be desirable to provide a presbyopic contact lens with elimination of haziness or blur in the field of vision.
The problems suggested in the preceding are not intended to be exhaustive, but rather are among many which might tend to reduce the effectiveness and presbyopic patient satisfaction with previously known multifocal contact lenses. Other noteworthy problems may also exist; however, those presented above should be sufficient to demonstrate that multifocal contact lenses appearing in the past will admit to worthwhile improvement.